Neurodegenerative diseases are a group of diseases typified by deterioration of neurons or their myelin sheath. This destruction of neurons eventually leads to dysfunction and disabilities. Often times inflammation is found to be a component of neurodegenerative diseases and adds to the pathogenesis of the neurodegeneration (Minagar, et al. (2002) J. Neurological Sci. 202:13-23; Antel and Owens (1999) J. Neuroimmunol. 100: 181-189; Elliott (2001) Mol. Brain. Res. 95:172-178; Nakamura (2002) Biol. Pharm. Bull. 25:945-953; Whitton P S. (2007) Br J Pharmacol. 150:963-76). Collectively, these diseases comprise the art-recognized inflammatory neurodegenerative diseases. Neuroinflammation may occur years prior to any considerable loss of neurons in some neurodegenerative disorders (Tansey et. al., Fron Bioscience 13:709-717, 2008). Many different types of immune cells, including macrophages, neutrophils, T cells, astrocytes, and microglia, can contributed to the pathology of immune-related diseases, like Multiple Sclerosis (M.S.), Parkinson's disease, amyloidosis (e.g., Alzheimer's disease), amyotrophic lateral sclerosis (ALS), prion diseases, and HIV-associated dementia. More specifically, research groups have noted that in MS the injury to myelin is mediated by an inflammatory response (Ruffini et. al. (2004) Am J Pathol 164:1519-1522) and that M.S. pathogenesis is exacerbated when leukocytes infiltrate the CNS (Dos Santos et. al. (2008) J Neuroinflammation 5:49). One research group has developed genetic models to test CNS inflammation and its effects in MS (through the animal model experimental autoimmune encephalomyelitis (EAE). In addition, pro-inflammatory cytokines (specifically TNF-alpha) were found to be elevated in Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis (ALS). (Greig et al (2006) Ann NY Acad of Sci 1035:290-315). These inflammatory neurodegenerative diseases may, therefore, be effectively treated by anti-inflammatory drugs.
Inflammatory neurodegenerative diseases include but are not limited to: multiple sclerosis (MS), Parkinson's disease, amyloidosis (e.g., Alzheimer's disease), amyotrophic lateral sclerosis (ALS), HIV-associated dementia, stroke/cerebral ischemia, head trauma, spinal cord injury, Huntington's disease, migraine, cerebral amyloid angiopathy, AIDS, age-related cognitive decline; mild cognitive impairment and prion diseases in a mammal.
Multiple sclerosis (MS) is a chronic inflammatory neurodegenerative disease of the central nervous system (CNS) that affects approximately 1,100,000 people all over the world, in particular affects young adults (Pugliatti et al. (2002) Clin. Neurol. Neuros. 104:182-191). MS is characterized pathologically by demyelination of neural tissue, which results clinically in one of many forms of the disease, ranging from benign to chronic-progressive patterns of the disease state. More specifically, five main forms of multiple sclerosis have been described: 1) benign multiple sclerosis; 2) relapsing-remitting multiple sclerosis (RRMS); 3) secondary progressive multiple sclerosis (SPMS); 4) primary progressive multiple sclerosis (PPMS); and 5) progressive-relapsing multiple sclerosis (PRMS). Chronic progressive multiple sclerosis is a term used to collectively refer to SPMS, PPMS, and PRMS. The relapsing forms of multiple sclerosis are SPMS with superimposed relapses, RRMS and PRMS.
Throughout the course of the disease there is a progressive destruction of the myelin sheath surrounding axons. Since intact myelin is essential in the preservation of axonal integrity (Dubois-Dalcq et al., Neuron. 48, 9-12 (2005)) systematic destruction eventually leads, clinically, to various neurological dysfunctions including numbness and pain, problems with coordination and balance, blindness, and general cognitive impairment. Interestingly, MS progression can differ considerably in patients with some having slight disability even after several decades of living with the disease, while others becoming dependent upon a wheelchair only a few years after being diagnosis.
The etiology of MS currently is unknown, but studies examining genetic evidence, the molecular basis, and immunology factors are beginning to elucidate the course of the disease and the mechanism by which demyelination occurs. In genetic analyses, some reports have indicated that related individuals have higher incidence of MS when compared to normal population (0.1% prevalence of MS): an identical twin having a 30% chance of developing the disease if the other twin has MS and fraternal twins and siblings have a 1-2% chance if a another sibling is affected by MS. Several groups have utilized linkage and association studies to discover the genes responsible for this heritability and found that the relative risk of being affected by MS is 3-4 fold higher to those carrying a the major histocompatibility complex (MHC) class II allele of the human leukocyte antigen (HLA)-DR2 allele. Other genes have been identified that associate with MS, but a much lower risk. The link between MS susceptibility and MHC Class II strongly suggests a role for CD4+ T-cells in the pathogenesis of MS (Oksenberg et al., JAMA 270:2363-2369 (1993); Olerup et al., Tissue Antigens 38:1-3 (1991)).
In addition, identification of genes that are differentially expressed in MS patients suffering from MS compared to healthy individuals has been attempted. Gene microarrays have been used 1) to examine transcription from MS plaque types (acute verses chronic) and plaque regions (active verses inactive) (Lock and Heller (2003)); 2) to compare peripheral blood mononucleocytes (PBMC) in RRMS patients verses controls, from patients both with and without interferon-β treatment (Sturzebecher et al. (2003)); and 3) to examine CNS cells in stages of experimental allergic encephalomyelitis (EAE) in mice, an animal model of MS (Lock et al. (2002)). Much of what these experiments discovered was expected, including the finding that anti-inflammatory, anti-apoptotic genes are down-regulated and pro-inflammatory, proliferation genes are up-regulated. Surprising results include identification of potential novel targets for therapeutic application such as osteopontin (Chabas et al. 2001) and TRAIL (Wandinger et al. 2003)). However, many of the genes that have differential regulation when comparing expression from MS patients with healthy individuals have unknown significance in MS development, because any genes that may affect MS susceptibility and/or progression are still unknown.
Further research has determined that inflammatory responses initiated by autoreactive CD4+ T-cells can mediate injury to myelin (Bruck et al., J. Neurol. 206:181-185 (2003)). In general, it is believed that much of the damage occurring to myelin sheaths and axons during an episode of MS happens through autoreactive T cell response which produces an inflammatory response including the secretion of proinflammatory (e.g. Th1 and Th17) cytokines (Prat et al., J. Rehabil. Res. Dev. 39:187-199 (2002); Hemmer et al., Nat. Rev. Neurosci. 3:291-301 (2002)).
Treatments that currently are available for MS include glatiramer acetate, interferon-β, natalizumab, and mitoxanthrone. In general, these drugs suppress the immune system in a nonspecific fashion and only marginally limit the overall progression of disease. (Lubetzki et al. (2005), Curr. Opin. Neurol. 18:237-244). Thus, there exists a need for developing therapeutic strategies to better treat MS.
Glatiramer acetate is composed of glutamic acid, lysine, alanine, and tyrosine as a random polymer. Glatiramer acetate has limited effectiveness and significant side effects, for example, lump at the site of injection, chills, fever, aches, shortness of breath, rapid heartbeat and anxiety. In an important clinical study using 943 patients with primary progressive MS, glatiramer acetate failed to halt the progression of disability and the disease (Wolinsky, et al (2007) Ann Neurol 61:13-24).
Interferon-β is a naturally occurring protein produced by fibroblasts and part of the innate immune response. As a drug for MS, interferon-β is about 18-38% effective in reducing the rate of MS episodes. Side effects include mild ones flu-like symptoms and reactions at the site of injection and more serious (e.g., depression, seizures, and liver problems)
Mitoxantrone is a treatment for MS. It was developed as a chemotherapy treatment for use in combating cancer—working by interfering with DNA repair and synthesis and is not specific to cancer cells. Side effects from mitoxantrone can be quite severe and include nausea, vomiting, hair loss, heart damage, and immunosuppression.
Natalizumab is a humanized monoclonal antibody that targets alpha4-integren, which is a cellular adhesion molecule. Natalizumab is believed to work by keeping immune cells that cause inflammation from crossing the blood brain barrier (BBB). Side effects include fatigue, headache, nausea, colds, and allergic reactions.
Parkinson's disease, another inflammatory neurodegeneration disease, is characterized by movement disorders, including muscle rigidity and slow physical movements. Recent research into Parkinson's disease has observed that due to enhanced expression of cytokines and HLA-DR antigens it is likely that the immune response contributes to the neuronal damage (Czlonkowska et. al. (2002) Med Sci Monit 8:RA165-77).
Amyloidosis develops when certain proteins have altered structure and tend to bind to each building up in particular tissue and blocking the normal tissue functioning. These altered structured proteins are called amyloids. Often amyloidoses is split into two categories: primary or secondary. Primary amyloidoses occur from an illness with improper immune cell function. Secondary amyloidoses usually arise from a complication of some other chronic infectious or inflammatory diseases. Examples of such include Alzheimer's disease and rheumatoid arthritis. Since the underlying problem in secondary amyloidosis is inflammation, treating inflammation likely will be beneficial.
Alzheimer's disease is another type of inflammatory neurodegenerative disease. It is exemplified by the increasing impairment of learning and memory, although the disease may manifest itself in other ways indicating altered cognitive ability. Throughout the disease the progressive loss of neurons and synapses in the cerebral cortex leads to gross atrophy of the neural tissue. Although the cause of Alzheimer's is unknown, many believe that inflammation plays an important role and clinical studies have shown that inflammation considerably contributes to the pathogenesis of the disease (Akiyama, et. al. (2000) Neurobiol Aging. 21:383-421.
In amyotrophic lateral sclerosis, a link between inflammation and the disease has been suggested (Centonze, et. al. (2007) Trends Pharm Sci 28:180-7). In addition, TNF-alpha mRNA has been found to be expressed in spinal cords of a transgenic mouse model for amyotrophic lateral sclerosis. Interestingly, the transcript was detected as early as prior to onset motor difficulties until death caused by ALS (Elliot (2001) Brain Res Mol Brain Res 95:172-8).
Taupathies.
Tauopathies are a class of neurodegenerative diseases resulting from the pathological aggregation of tau protein in neurofibrillary tangles (NFT) in the human brain. Tau proteins are involved in stabilizing microtubules and are primarily located in neurons in the central nervous system. When tau proteins become defective, thus no longer stabilizing microtubules properly, they can result in dementias, such as Alzheimer's disease, argyorphilic grain disease, frontotemporal dementia, progressive supranuclear palsy, corticobasal degeneration, frontotemporal lobar degeneration (Pick's disease) and. dementia pugilistica (DP) (a.k.a., boxer's dementia, chronic boxer's encephalopathy) neurofibrillary tangles are at least implicated in DP). The non-Alzheimer's tauopathies listed above are sometimes grouped together as “Pick's complex”.